Vision begins with the absorption of light by rhodopsin. The conformational changes that this event induces in rhodopsin's cytoplasmic surface allows rhodopsin to interact with other components of the phototransduction cascade-transducin, rhodopsin kinase, and arrestin. The long-range goal of our research is to understand the molecular events of the recovery process following phototransduction. In this application, we seek to extend our knowledge of this recovery process through studies of the binding interaction between rhodopsin and arrestin. The rhodopsin/arrestin recovery process is a classical model system for a large class of G-protein-coupled receptors that are inactivated in an arrestin-dependent manner. In the visual system, mutations that disrupt the rhodopsin/arrestin interaction can lead to retinitis pigmentosa, and also stationary night blindness (in the case of arrestin). In its ground state, arrestin is inactive, unable to bind to photoactivated rhodopsin. Interaction with rhodopsin's phosphorylated carboxy-terminus induces a conformational change in arrestin that then allows it to bind to rhodopsin. This study is designed to develop an understanding of the molecular rearrangements that arrestin undergoes following activation. Specifically, we will address the following questions: A. What is the identity of the sites in the surface array of arrestin that bind to photoactivated rhodopsin? B. How are the sites of the binding array assembled? C. Where does the phosphorylated C-terminus of rhodopsin interact with arrestin to initiate this array assembly?